1. Field of the Invention
The present invention relates to small molecules having high affinity and specificity to prostrate-specific membrane antigen (PSMA) and methods of using them for diagnostic and therapeutic purposes.
2. Summary of the Related Art
Prostate-specific membrane antigen (PSMA) is uniquely overexpressed on the surface of prostate cancer cells as well as in the neovasculature of a variety of solid tumors. As a result, PSMA has attracted attention as a clinical biomarker for detection and management of prostate cancer. Generally, these approaches utilize an antibody specifically targeted at PSMA to direct imaging or therapeutic agents. For example, ProstaScint (Cytogen, Philadelphia, Pa.), which has been approved by the FDA for the detection and imaging of prostate cancer, utilizes an antibody to deliver a chelated radioisotope (Indium-111). However, it is now recognized that the ProstaScint technology is limited to the detection of dead cells and therefore its clinical relevance is questionable.
The success of cancer diagnosis and therapy using antibodies is limited by challenges such as slow elimination of these biomolecules from the blood and poor vascular permeability. In addition, large antibodies bound to cell-surface targets present a barrier for subsequent binding of additional antibodies at neighboring cell-surface sites resulting in a decreased cell-surface labeling.
In addition to serving as a cell-surface target for antibodies delivering diagnostic or therapeutic agents, a largely overlooked and unique property of PSMA is its enzymatic activity. That is, PSMA is capable of recognizing and processing molecules as small as dipeptides. Despite the existence of this property, it has been largely unexplored in terms of the development of novel diagnostic and therapeutic strategies. There are a few recent examples in the literature that have described results in detecting prostate cancer cells using labeled small-molecule inhibitors of PSMA.
Certain phosphoramidate PSMA inhibitors have been described in U.S. Pat. No. 7,696,185 to Berkman.